Chapter 5.2 Calorimetry

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1

Calorimetry

card image

a technique used to measure the amount of heat involved in a chemical or physical process

used to measure amounts of heat transferred to or from a substance

2

system

substance undergoing the chemical or physical change

3

surroundings

the other components of the measurement apparatus

that serve to either provide or absorb heat from the system

4

calorimeter

device used to measure the amount of heat involved in a chemical or physical process

5

How do readings of a calorimeter help calculate the amount of heat change?

the heat is either raised or decreased in a calorimeter

the temp change (ΔT) along w/ specif heat (c) and mass (m) of the soln

can be used to calculate the amount of heat involved in either type

of process (exo or endo)

6

Describe calorimeters

- well-insulated to prevent the transfer of heat w/ outside enviornment

- can be made w/ 2 polystyrene coffee cups (less accurate b/c more heat exchange w/ outside environment - usu include a stirrer

- more expensive ones used for industry and research= more accurate

7

Under ideal circumstances, what is the net heat change of two substances?

qsubstanceM + qsubstanceW = 0

...

qsubstanceM= -qsubstanceW

8

What does the negative sign indicate in the relationship btwn substances?

it merely shows that they are opposite in direction of heat flow (gain or loss)

9

What determines the arithmetic sign of the q (heat) value?

by whether the matter in question gains or loses heat

in ex: qmetal was negative b/c it lost heat= -qmetal

10

When is it not okay to neglect very small amounts of heat absorbed by the calorimeter?

not for highly accurate measures

11

What does the calorimeter do when working with chemical reactions?

minimizes energy exchange w/ the environment

12

Explain the chemical reaction heat formula

heat produced/consumed in the reaction "system" [qreaction]

plus the heat absorbed/lost by solution "surroundings" [qsolution]

must add up to zero

qreaction + qsolution= 0

13

Chemical heat reaction formula

What does it mean?

This means that the amount of heat produced/consumed = the amount of heat absorbed/lost by the solution

qreaction = -qsolution

14

What happens when amount of heat of calorimeter is too large to neglect or if more accurate results are needed?

must take into account heat absorbed both by the solution and calorimeter

15

bomb calorimeter

used to measure the energy produced by reactions that yield large amounts of heat and gaseous products, such as combustion rxns

it operates at constant volume